Drilling tools are used when drilling a well in the subterranean formation. However, drilling may also be performed in an existing well for reboring a stuck valve or for taking out a sample of the formation.
U.S. Pat. No. 2,643,858 discloses a drilling tool for taking out a sample. For this purpose, the drilling tool is arranged with lifting fingers which are lowered for engaging the sample after this has been cut out. The disclosed drilling tool has a very complicated design for taking out the sample, where the arms may break or get stuck during a drilling operation.
Occasionally, a valve downhole which has been closed for some time gets stuck due to corrosion or the like, and thus cannot be reopened with normally used equipment. In such situations, reboring of the stuck valve is the only solution. When reboring the stuck valve, the drill bit tends to slide on the abutting surface, especially if the valve is a ball valve.